Air-dropped cargo pallets do not always land in designated locations. Finding them in GPS denied environments, in darkness, in adverse weather, or on rough terrain is difficult and dangerous. An inexpensive tag or drop zone beacon identifying the cargo is needed that would radiate a signal from which the recipient could determine the proximity and direction of the pallet.
Paratroopers jumping from airplanes usually convene at a designated location before beginning their mission. GPS is the preferred approach for the individual to find the “rally point.” There are areas where GPS reception is poor or unavailable such as in heavily wooded or mountainous areas or in urban areas. For this, a rally point beacon, similar to the drop zone beacon, would emit a signal towards which the paratrooper would move.
Conventional methods place low duty cycle VHF and UHF beacons on the cargo which can be tracked from land, air or space. The beacons can also relay the GPS position of the cargo. Other systems that have been utilized are similar to LoJack® (auto anti-theft device), active tags used for tracking wildlife, or similar pet collars with homing radios. LoJack® is a registered trademark of LoJack Corporation in Westwood, Mass.
Most deployed comms systems operate at frequencies above 30 MHz where point-to-point communications is dependent on line-of-sight propagation. Hence, obstructions such as hills, trees, and metal buildings can prevent the communications link to close. HF comms (2-30) MHz are not reliable for near-in links because sky wave propagation can cause the signal to “skip over” a nearby receiver. Propagation conditions can also change dramatically between day and night and during sun spot activity.
Previous approaches relied heavily on perfect conditions, such as upright landings, smooth terrain with no obstacles where line-of sight (LOS) communications (comms) are possible for several kilometers (kms), for acquiring GPS coordinates and communicating position. In cases where only beacons are possible, directing airborne or national assets to track regular cargo such as K-rations, ammunition, or fuel is not cost effective. Unless direct LOS comms are possible, direction finding schemes using simple, low-cost receivers to locate the beacons are very susceptible to multipath ambiguities.
Furthermore, smart GPS-guided parachutes often go astray leaving cargo drops widely dispersed on the ground. The placement of VHF, UHF, and microwave beacons or tags has not been very successful because communications at these frequencies is dependent on line-of-sight (LOS) propagation with little to no blockage between the beacon and the soldier-held receiver.
There is a need for guaranteed short range communications in various field and battle space applications.